The present invention is directed to a method of producing a strip of material having longitudinally continous portions, the thickness of which varies in the direction of width of the strip, that is, a strip having a non-uniform cross section, by a rolling process.
It is well known that if a blank of uniform thickness is rolled with a partially changed reduction rate to provide a strip having a non-uniform cross section, the amount of deformation of the material is locally different and the difference in the amount of deformation results in a difference in longitudinal expansion of the rolled strip, thereby causing the occurrance of meandering or twisting in the rolled strip.
In order to solve the problem of meandering or twisting, a lateral rolling method was employed to cause the deformed material to flow in the direction of width of the blank or an expanding rolling method was employed. In the lateral rolling method, however, the blank is rolled in a direction perpendicular to the longitudinal direction of the blank and therefore it is necessary to intermittently feed the blank material. This results in a deterioration of the working properties of the material and considerably reduces the production rate. In the expanding rolling method, on the other hand, in which the thickness of the material is changed in the direction of width by a reduction process using a combination of the V-shaped die and a roll, the reduction force is produced by causing the roll to perform a reciprocating motion. Therefore, the processing of the strips must take place intermittently and it is impossible to achieve a high speed, efficient rate of production.